1. Field of Invention
The present invention relates generally to the production of bent sheets and more particularly to a stop assembly for positioning glass sheets that are pressed between upper and lower shaping molds.
2a. Technical Considerations
Bent glass sheets are commonly used as glazed enclosures in vehicles such as automobiles and the like. For such applications, the glass sheets must be bent to precisely defined curvatures dictated by the configuration and outline of the vehicle openings in which the sheets are to be installed, as well as the overall styling of the vehicle. At the same time, it is important that the bent sheets meet very stringent optical requirements so that the viewing area of the resulting shaped window is free of optical defects that would interfere with good vision through the window. For certain windows used as glazed enclosures, bent glass sheets are tempered to strengthen them and increase their resistance to damage resulting from impact. The particles resulting from the breakage of tempered glass are relatively small and smoothly surfaced, and thus are less likely to cause damage to an occupant of a vehicle than untempered glass, which fractures under less severe loads and causes particles having jagged edges of a larger particle size that are more likely to injure vehicle occupants.
In the glass sheet bending art, the glass sheet can be supported and press bent in a horizontal position. The glass sheets are generally supported, either on a series of conveyor rolls or by a gaseous hearth bed which supports the glass in close relation thereover by hot gas. The glass is then lifted from proximity to the support plane into engagement with a vacuum holder and then deposited onto a ring-like member, which is interposed between the plane of support and the bottom surface of the vacuum holder. The need for a glass sheet alignment member becomes increasingly more critical when the glass sheet is to be shaped to a complicated shape defined by a downwardly facing surface of a vacuum mold and an upwardly facing surface of complimentary shape of a vertically movable outline lifting mold. Furthermore, when the heat softened glass sheet is shaped by moving it over a gas hearth bed having a downwardly curved downstream end portion that curves downward to cause the glass sheet to flow downward and sag along its leading edge portion, it is important to have alignment means in position to engage the leading edge of the glass sheet even when the vertically movable outline mold occupies a recessed position. It is equally important that once the glass sheet is properly aligned, it remain aligned until it is lifted off the support surface and is fully engaged by the vertically movable outline mold.
2b. Patents of Interest
U.S. Pat. Nos. 2,695,476 and 2,798,338 to Jendrisak and U.S. Pat. No. 2,729,032 to White disclose outline molds that have glass edge engaging members that pivot inward to follow the edges of the glass sheet as it sags towards the outline mold. The glass sheet engaging members must be removed manually to remove the bent glass sheet from the mold.
U.S. Pat. Nos. 2,814,164 and 3,089,319 to Carson and White disclose outline molds having universally pivotable stops that follow and engage pointed tips at the opposite longitudinal edges of glass sheets supported for bending on the outline mold, to control tip over bending as well as positioning.
U.S. Pat. No. 2,840,953 to Black discloses bimetal actuators attached to glass edge guide members to change the location of the guide members in response to a change in temperature during the bending cycle. When the mold is cool, the bimetal actuators position the edge guides into proper positions for aligning a glass sheet edge. When the mold is heated to heat soften the glass, the bimetal actuators move the edge guide members out of contact with the glass, thus losing the contact between the guide members and the glass sheet edge that maintains the glass in proper mold alignment.
U.S. Pat. No. 2,901,866 to McKelvey discloses outline molds with counterweighted, pivoted glass engaging members that pivot against the glass sheet edge as the glass sags toward the shaping surface of the outline mold. No provision is made to disengage the glass edge after the glass bend is completed except for manual operation.
U.S. Pat. No. 3,220,822 to Jendrisak discloses sectionalized outline molds having a pivoted end portion for each end mold section that follow the ends of the glass sheet as the latter shortens from a flat shape to a shaped curved in elevation. Manual operation is also required here to separate the end portions from the bent glass sheet.
U.S. Pat. No. 3,230,067 to Carson and Stickel discloses an outline sectionalized shaping mold comprising pivotally supported shaped members that serve both as edge guides and supports for the flat glass sheet that rotate outwardly from the guide side edges as the mold closes and the glass sheet sags. Outward rotation permits the likelihood of glass sheet misalignment during shaping.
U.S. Pat. No. 4,272,275 to Reese discloses an apparatus for press bending glass sheets that are sag bent in an outline shape of an outline mold and are conveyed into a compound bending station having upper and lower press bending molds of complicated shape including a transverse bend of an S-shaped configuration. There, the lower press bending mold lifts the preliminarily bent glass sheet into engagement with the upper press bending mold to develop a compound glass sheet shape. The lower press bending mold lowers to redeposit the compound bent glass onto the lower mold. The apparatus of this patents includes glass edge engaging members for the outline mold that occupy a glass engaging position during one phase of the shaping cycle (such as when the glass is initially conveyed on the outline mold to develop a longitudinal component of bend) and are automatically removed from glass edge engagement immediately before the longitudinally bent glass is lifted from the outline mold for further processing. Such glass edge engaging members cannot continue to align the glass sheet on the outline mold when returned thereto after further processing. In addition, the glass edge engagement members are reset in proper position by hand for a subsequent cycle.
It would be beneficial for the glass sheet shaping art to develop apparatus for bending glass sheets to a compound bend that includes glass edge alignment members that establish a position of alignment for a glass sheet arriving at a shaping station and remains in place until immediately prior to when the lower outline mold engages an upper vacuum mold without causing damage to the glass edge or any shaping station part.